1. Field of the Invention
The present invention relates to a detachable lens block attachable and detachable to and from a camera block including an image pickup device and a video (picture) signal processing circuit, and more particularly to a detachable lens block equipped with at least an autofocus control function and a video camera system based upon the same.
2. Description of the Related Art
In a video camera system having an integral construction of a camera block and a lens block, in general an autofocus control function is provided to automatically accomplish the in-focus condition with respect to a subject. Particularly, in the case of a monitoring type video camera system, this function is available.
Japanese Examined Patent Publication No. 39-5265 discloses one example of video camera systems having such an autofocus control function. Referring to a schematic block diagram of FIG. 5, a description will be made hereinbelow of the arrangement of this prior example.
In FIG. 5, a subject image coming through an optical lens 45 is incident on an image pickup device 40 to be converted into an electric signal serving as a video signal. This video signal is processed in a signal processing circuit 41 comprising a preamplifier and a process amplifier and then given to a video signal converting circuit 42 where, through processing such as the addition of a synchronizing signal and the synthesis of a color-difference signal, the video signal is converted into a composite video signal meeting the standard mode such as NTSC and PAL.
On the other hand, the video signal outputted from the signal processing circuit 41 is also fed to an AF (autofocus control) circuit 43. This AF circuit 43 is composed of a differentiating circuit for detecting a rising edge of the video signal and a peak (maximum) point detecting circuit to produce a focus control signal indicative of the degree of the in-focus condition. This focus control signal is forwarded to a lens drive unit 44 which is for the purpose of moving the optical lens 45 in its optical-axis directions in accordance with the focus control signal (in Japanese Examined Patent Publication No. 39-5265, the image pickup device 40 is shifted in the optical-axis directions of the optical lens 45), and which is made up of a mechanism section such as a motor and gears, a servo amplifier for creating a motor drive signal on the basis of the focus control signal, and others.
In this arrangement, the AF circuit 43 monitors the amplitude of the rising edge of a video signal and outputs, to the lens drive unit 44, a focus control signal for the movement of the optical lens 45 in the direction that this amplitude increases. When the amplitude of the rising edge of the video signal reaches the peak point due to the movement of the optical lens 45, a decision is made to the in-focus condition, thus stopping the optical lens 45.
Furthermore, Japanese Examined Patent Publication No. 7-54969 discloses another example of video camera systems having an autofocus feature, where a focusing lens is oscillated in a narrow range in its optical-axis directions in accordance with a high-frequency reference signal so that the decision on the in-focus condition is made on the basis of the relation in phase between the component (oscillation component) due to the oscillation, included in a video signal outputted from an image pickup device, and the reference signal or a decision is made on the direction of moving an optical lens to assume the in-focus condition.
Accordingly, the aforesaid oscillation component is extracted from the video signal outputted from the image pickup device and processed in a preamplifier. The extracted oscillation signal is detected in synchronism with the aforesaid reference signal to detect the phase relation between the oscillation component and the reference signal, thereby deciding the direction of the movement of the optical lens for the in-focus condition. If the optical lens moves to pass through the in-focus point, the phase of the oscillation component is inverted, which allows the detection of the in-focus condition.
In the recent situation, in addition to the above-mentioned autofocus control function, the prior video camera systems have been equipped with an automatic iris control function which controls the iris in accordance with the fluctuation of brightness in the camera-using place so that a video signal with a constant intensity is always obtainable and further provided with a zoom control function, thereby achieving the easier-to-use of the system and providing higher-quality picture.
Furthermore, preferably the video camera systems has a structure which allows the interchange between optical lenses having different zooming magnifications. Particularly, in the case of an observational type video camera system, it is necessary to use an optical lens having a zooming magnification conforming with the environment (for example, the area of the monitoring space) in the camera-using place.
For meeting this requirement, it is considered that the video camera system is attachably and detachably divided into a block comprising a camera (which will be referred hereinafter to as a camera block) and a block including an optical lens (which will be referred hereinafter to as a lens block).
Referring again to FIG. 5, a brief description will be made hereinbelow of the division of this video camera system.
In FIG. 5, the camera block is a portion surrounded by a dotted line, including the image pickup device 40, the signal processing circuit 41, the video signal converting circuit 42 and the AF circuit 43, whereas the lens block is the other portion including the optical lens 45 and the lens drive unit 44. The camera block and the lens block are attachable and detachable, for example, through the use of a screw coupling construction (C mount or CS mount).
However, this division structure causes the following problems, which will be mentioned with reference to FIG. 5.
First, a large number of connecting lines need to be placed between the camera block and the lens block.
That is, control lines 46 are necessary for sending a focus control signal from the AF circuit 43 to the lens drive unit 44. As the control lines 46, required are two lines: a transmission line for sending a control signal to move the optical lens in the infinitely far-end direction and a transmission line for feeding a control signal to shift it in the near-end direction. In addition, when the optical lens 45 reaches the infinitely far end or near end, there is a need to detect this fact and to forward an end detection signal to the AF circuit 43 for stopping the output of the focus control signal. For this reason, it is necessary to place two transmission lines for one of the infinitely far-end detection signal and the near-end detection signal, i.e., four in total (three when one is used in common), to send these end detection signals from the lens block to the AF circuit 43. Further, one power supply line and one grounding line are necessary for supplying a power voltage from the camera block side to the lens drive unit 44 of the lens block. In consequence, the equipment of the autofocus control function requires at least 7 or 8 connecting lines 46.
Moreover, if the camera system is additionally equipped with the iris control function and the zoom control function, the connecting lines further increases in number. In this case, although not shown in FIG. 5, an iris control circuit for producing an iris control signal is placed on the camera block side while an iris drive unit is located on the lens block side, and therefore, one transmission line becomes necessary for sending this iris control signal. In addition, it is necessary to detect that the iris takes the maximum and minimum open conditions and further to send maximum/minimum iris open detection signals, which stop the output of the iris control signal from the iris control circuit, to an iris control system at the time of the detection. Accordingly, two transmission lines become necessary. That is, the iris control requires three connecting lines in total.
Furthermore, in the case of an observational type video camera system, a zoom adjusting signal is once forwarded from an external controller to the camera block so that a zoom control signal is created on the basis of this zoom adjusting signal and fed to the lens block. In addition, when the zoom lens is at the telephoto end or the wide-angle end, an end detection signal is generated to be sent to the camera block, thereby inhibiting the generation of the zoom control signal. For this reason, as the connecting lines for the zoom control, required are one transmission line for the zoom control signal and four transmission lines for the end detection signals indicative of the fact that the zoom lens reaches the telephoto end and the wide-angle end (three when one is used in common). Thus, the zoom control requires four or five connecting lines.
As described above, if providing the autofocus control function, the iris control function and the zoom control function to the video camera system, at least 14 to 16 connecting lines become necessary between the camera block and the lens block. In general, the connecting lines are bundled and connected through connectors to the camera block and the lens block to be placed therebetween. However, if the number of connecting lines increases, not only the connectors enlarge in size but also the bundle of the connecting lines extremely increases in diameter. Particularly, considering that it is desired to reduce the size of the video camera system by the size-reduction of the camera block and the lens block, the large-diameter connecting line bundle and large-sized connectors are not preferable as products, and hence, difficulty is encountered to actually put it as a product into production.
In the second place, in video camera systems, in general the camera lens sections are produced by optic manufacturers, whereas the camera bodies are produced by the electronic makers. In the case of attachably and detachably dividing the video camera system shown in FIG. 5 into the lens block and the camera block, the camera block is designed and produced by an electronic manufacturer while the lens block is designed and produced by an optic maker. Further, the user can desire various kinds of lens blocks having different magnifications, autofocus control functions, iris control functions and zoom control functions, and therefore, for satisfying such structural requirements it is preferable that different kinds of lens blocks are mountable onto one camera block. In the case of the video camera systems, it has advantage of the kind of the lens block being selected in accordance with the environment or the like in the camera-locating place.
However, different kinds of lens blocks have different characteristics from one another. Even if lens blocks are the same kind, lens blocks made by different makers have slightly different characteristics from one another. Accordingly, in cases where the selected lens block is set to the camera block, there is a possibility that the circuit characteristics of the lens drive unit, for example, of the lens block does not sufficiently match with the circuit characteristics of the AF circuit of the camera block, so that the desired function does not satisfactorily work.
For instance, in FIG. 5, in the case of the division of the video camera system mentioned above, for the lens block, the optic maker sets the optical characteristic of the optical lens 45 and further sets the circuit characteristic of the lens drive unit 44 in accordance with the movement characteristic at the focus control, whereas for the camera block the electronic maker makes the AF circuit 43 have the circuit characteristic agreeing with a video signal with a standardized level from the signal processing circuit 41. However, if this lens block is attached to the camera block, the focus control signal from the AF circuit 43 does not always coincide with the focus control signal, the lens drive unit 44 needs, with a high accuracy, with the result that a difference can occur between the lens blocks to be put to use.